This invention pertains generally to the fabrication of optical elements and particularly to a method of making elements wherein the optical characteristics are controlled.
It has been known for some years in the field of fiber optics that certain lens-like elements (sometimes referred to as "channelplates" or "collimators") may advantageously be used to filter light. For example, in my copending application Ser. No. 726,079 entitled "Optical Apparatus", filed Sept. 23, 1976 U.S. Pat. No. 4,183,664 and assigned to the same assignee as this invention, a foraminous plate wherein the walls of the individual foramina are rendered opaque may be used to pass light originating in a small selected field and to reject light from any point outside such field.
Unfortunately, when the above-mentioned foraminous plate is made according to any known method, it is very difficult and expensive to fabricate a satisfactory plate. The dimensions of the individual ones of the foramina, coupled with the requirement that the inner wall of each foramen be substantially the same as each other one, explain why known methods are difficult and expensive. For example, in a typical case where it is desired to define a field of view with an angular size in the order 1.degree. and each foramen is cylindrical, with a diameter say of 400.times.10.sup.-6 inches, the length of each foramen must be approximately 22,800.times.10.sup.-6 inches or 0.023 inches in length. For proper operation, the optical characteristics of the wall of each foramen must be the same along its length, i.e. the wall must be totally nonreflective or reflective or have some other desired characteristic. It is manifest, then, that any treatment of the walls of the literally thousands of foramina making up a channelplate of modest size (there being about 202,800 foramina in a channelplate of 1" diameter) is most difficult when, as is now the practice, such foramina are made by drawing bundles of hollow optical tubing or by treating photosensitive glass.